This invention relates generally to electric motors, and more particularly to rotor position sensing assemblies within electric motors.
Some electric motors require a rotor position-sensing device for proper operation. The rotor position sensing devices provide information to a motor controller. In order to provide reliable information, the sensors need to be positioned very accurately, otherwise the motor may fail to run or may run inefficiently.
Hall effect devices are ubiquitous in automotive, aircraft, appliance and tool applications where non-contact sensing is required. Hall effect devices are sensors that detect motion, position or change in field strength of an electromagnet, a permanent magnet, or a ferromagnetic material with an applied magnetic bias. Electric motors typically use electromagnetic fields to create torque or force. It is known to use hall effect devices in electric motors to sense a position of a rotor magnet. The hall effect device must be accurately positioned relative to the midpoint of the rotor magnet. Displaced hall effect devices can produce hysteresis and motor current discontinuities that disturb torque.
It would be desirable to provide a method and system for mounting a rotor position sensor that reliably and accurately mounts a sensor within an electric motor rotor at a low cost.
In an exemplary embodiment of the invention, a rotor position sensor assembly includes a housing, a hall effect device, a printed circuit board, a plurality of leads, and a cable tie. The housing includes two pairs of guides that fixedly attach the housing to a stator end cap and a plurality of stator laminations.
More particularly, the housing includes a bottom wall, a pair of first side walls extending from the bottom wall, a first pair of housing guides extending from the first sides walls, a top wall, a pair of second side walls connecting the first side walls with the top wall, and a second pair of housing guides extending from the second side walls. The first side walls extend substantially perpendicularly to the bottom wall and the top wall extends substantially parallel to bottom wall. The second pair of housing guides is substantially flush with the top wall.
A gap extends between the first pair of housing guides and the second pair of housing guides. The first pair of housing guides has a wedge shape. A step extends from the bottom wall into a housing cavity. In addition, a pair of internal guides extend from the second side walls into the cavity such that the internal guides form the cavity into a substantially inverted T at a first end of the housing.
The housing is formed of a resilient material and attaches to a stator end cap with a snap-fit relationship. The housing attaches to the stator end cap quickly and easily and provides a secure fit between the stator end cap and the sensor housing.